This invention concerns articulated harvesters and, more particularly, a hinge arrangement for connecting front and rear bogies of such harvesters so as to provide for steering and for oscillation when traversing uneven ground.
An articulated harvester, compared with a conventional rigid chassis machine of similar size and capacity, has recognized advantages. These include better maneuverability and greater stability on side slopes and are especially valuable in relatively tall, bulky machines such as combine harvesters. These advantages depend at least in part, on a form of articulation or hinge arrangement permitting oscillation between the bogies when traversing uneven ground. For the vehicle to be most responsive to irregular surfaces and to minimize internal forces during oscillation, the (fore-and-aft) oscillation axis defined by the hinge arrangement should be close to the ground. This of course tends to magnify the relative lateral displacement between adjacent upper portions of the front and rear bogies which must take place during oscillation. If, as is known in some articulated vehicles, a simple short single link, essentially extending between the respective rear and front walls of the front and rear bogies, constitutes the upper portion of the hinge arrangement then, during oscillation, "foreshortening" of the link will cause inconvenient and possibly unacceptable kneeling or tipping of the bogies, so that the upper portions of the bogies will approach each other. Sufficient nominal clearance must be provided to avoid interference between the bogies but for compactness and efficiency in operation it is desirable to minimize the clearance between the bogies. In an earlier U.S. patent application, Ser. No. 020,863 now U.S. Pat. No. 4,317,326 also assigned to the assignee of the present invention, a compound linkage arrangement was proposed as an improvement over a conventional top link (also disclosed in that application) for minimizing, if not eliminating, the tendency to kneeling between the bogies during oscillation. But this solution is relatively heavy, bulky and complex and requires a number of extra pivots which involves the use of relatively close tolerance, somewhat expensive joints if "chucking" and instability are to be avoided.